A vast swath of icy sea, barrier islands and coastal land on Alaska's oil-rich North Slope will be granted special protection because of its importance to the threatened polar bear, under a proposal released Thursday by the U.S. Fish and Wildlife Service.

The agency proposes that 200,000 square miles (518,000 sq km) of coastline and shallow Arctic Ocean waters be designated as critical habitat, a status of heightened protection afforded under the Endangered Species Act.

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The area, which would be the largest ever designated for an Endangered Species Act-listed population, overlaps the territory with the largest existing oil fields in the United States where companies operate and plan to explore more.

Tom Strickland, assistant Interior Secretary for Fish, Wildlife and Parks, said in a telephone news conference that the critical-habitat designation should not hinder further development as long as operations are responsible and careful.